Abstract
Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a rare autoimmune disorder characterised by a spectrum of neuropsychiatric manifestations, movement and language disturbances, autonomic dysfunction, and coma. Its heterogeneous presentation poses a significant diagnostic challenge and is frequently misinterpreted as a primary psychiatric illness or infectious meningoencephalitis. We present the case of a 26-year-old woman with an acute onset of prominent psychiatric symptoms, initially raising suspicion for a primary psychiatric disorder. The psychiatric team, however, suspected the possibility of an organic etiology, prompting empirical antiviral and antibiotic therapy for presumed infectious meningoencephalitis. Despite these treatments, her condition deteriorated, with declining Glasgow Coma Scale (GCS) scores, autonomic instability, and seizure-like activity, necessitating intensive care unit (ICU) admission. Immunotherapy was initiated for suspected autoimmune encephalitis, particularly in the context of negative cerebrospinal fluid (CSF) viral polymerase chain reaction (PCR) results. Further imaging revealed an ovarian teratoma. Due to limited response to first-line immunotherapy, rituximab was introduced, and the teratoma was surgically resected. This combined approach led to gradual but sustained clinical improvement. Later, the CSF autoimmune panel confirmed the presence of anti-NMDAR antibodies. This case underscores the importance of considering anti-NMDAR encephalitis in patients presenting with acute psychiatric symptoms and highlights the value of a multidisciplinary approach in facilitating early diagnosis and treatment, thereby improving outcomes and reducing disability. It also discusses the therapeutic dilemma of initiating immunotherapy in the context of possible infectious meningoencephalitis and emphasises the dual role of teratoma removal in both acute management and relapse prevention.